1. Technical Field
The invention relates to a coating for pistons, in particular a coating for the piston skirt of an internal combustion engine.
2. Related Art
Coatings for the piston shaft, also referred to as the piston skirt, should exhibit a high wear resistance with at the same time a low coefficient of friction. In particular, a high durability and wear resistance is required in engine operating states subject to a high degree of wear, such as repeated cold starts. In this connection, depletion of the coating in the load-bearing regions of the piston shaft should above all be avoided.
Various coatings for pistons of internal combustion engines arc known in the prior art.
For example, U.S. Pat. No. 5,486,299 describes a lubricant composition for coating the surface of pistons and/or cylinders of engines that use alcohol or non-petroleum based products as fuel. This lubricant composition comprises a mixture of graphite, MoS2 and PTFE in a matrix of a polyamide imide resin (PAI resin).
EP 1 469 050 A1 describes a coating composition for pistons, which is obtained by mixing uncured polyamide imide (PAI) with a solid lubricant such as PTFE, titanium oxide powder and a silane coupling agent.
DE 10 2005 026 664 A1 also describes a coating for a piston based on a PAI lacquer. This coating is PTFE-free and contains 5-15 wt. % zinc sulphide, 5-15 wt. % graphite or MoS2 and 5-15 wt. % TiO2. Both zinc sulphide and TiO2, are used in the form of fine particles with a particle size of ≦0.7 μm.
De 43 43 439 A1 describes a reciprocating piston arrangement, which comprises a piston with a piston skirt formed in the manner of a relief with webs, which are coated with a solid lubricant of graphite, MoS2 and BN in an epoxy resin.
EP 0 976 795 A2 describes a corrosion protection lubricant for hinges and the like, which contains as lubricant a mixture of phenolic resin, epoxy resin, polyvinyl butyral resin and polyolefin wax. The coating also contains aluminium particles, zinc particles or a metal phosphate as corrosion inhibitor, and a solvent.
DE 103 29 228 A1 describes a polymer composite material for slide bearings with a polymer matrix that can, for example, consist of epoxy resin or PEEK. A filler material and nanoscale particles are embedded in this polymer matrix. Aramide fibers, glass fibers, carbon fibers, glass spheres, PTFE, graphite and silicones can be used as filler material. The nanoscale particles can be formed by TiO2, Al2O3, MgO, ZeO2, SiC, Si3N4, BN, glasses and hard solid metallic materials.